Zone condition controller and method of using same

ABSTRACT

An electrically-powered zone condition control apparatus includes a first multiplexing means adapted for receiving analog status signals emanating from a plurality of passive signaling devices such as temperature or humidity sensors or potentiometers and transmitting these status signals in multiplex fashion to an analog-to-digital converter. The converter changes these analog status signals to digital data signals and directs them to a microcomputer. A second multiplexing means receives binary input signals which may indicate, for example, that an electrical contact is open or closed and also transmits these signals in multiplex fashion to the microcomputer. The microcomputer is adapted to perform algorithmic decisional functions relative to the signals received therein and is adaptable to periodically, selectively transmit digital output signals to one or more of a plurality of digitally-addressable load devices coupled to it by a two-wire communication bus. The microcomputer is also adaptable to periodically receive digital input signals from one or more of the load devices. 
     A method for controlling a condition in a zone, temperature for example, includes the steps of generating a plurality of signals representative of the status of a plurality of signalling devices, converting selected status signals to digital data signals and directing the data signals and unconverted status signals to a computing means such as a microcomputer. The microcomputer performs algorithmic decisional functions relative to the signals received thereat and periodically, selectively transmits digital output signals along a communication bus to one or more of a plurality of uniquely, digitally addressable load devices. Digital input signals are periodically received from one or more of the load devices.

BACKGROUND OF THE INVENTION

This application is a continuation-in-part of co-pending applicationSer. No. 06/505,224 filed on June 17, 1983 by the same inventive entityas this application and entitled "Zone Condition Controller and Methodof Using Same".

This invention relates generally to process control apparatus and moreparticularly to a first level zone condition control apparatus forcontrolling the operation of heating, ventilating, humidifying and airconditioning (HVAC) equipment to effect environmental conditioning.

Computerized control systems are in wide use for controlling a varietyof processes, petrochemical, power generation and steel making beingexemplary. Typically, each such process comprises a plurality of processsubsystems or zones which may have control requirements peculiar theretoand which may be controlled by an apparatus dedicated to the properfunctioning of the particular zone. Such controllers are usually coupledto a more sophisticated, master controller disposed at a second orhigher hierarchical level within the overall control system and coupledto the first level controllers by a communication bus. For processeshaving a relatively small number of parameters to be sensed andcontrolled, it is desirable to employ a zone controller which isconstructed and arranged to define a less sophisticated and thereforeless expensive apparatus which is carefully matched to the parameters ofthe zone being controlled.

Another type of process which may require zone control or which may beadapted to control by zones includes environmental processes related toheating, ventilating, humidifying and air conditioning. Sophisticatedand relatively expensive hierarchical systems are known and in commonuse for controlling the HVAC systems in locations such as large officebuildings, universities, industrial complexes and the like. Such systemswill usually include a master control computer coupled to a number ofsubcontrollers which are distributed throughout a building and arecapable of more limited computerized function. These subcontrollers, inturn are typically coupled to a number of individual modules and loaddevices for controlling the HVAC equipment. While these systems providehighly acceptable performance in those installations, their complexityand resultant cost makes them undesirable for use in smaller HVACprocesses such as might be found in supermarkets, smaller warehouses,office buildings and the like. In constructions of this latter type, theHVAC equipment will typically include only a single set of interrelatedducts, termed an air handling unit, coupled to a zone or space, thetemperature and/or humidity environment of which is to be controlled.While these spaces are most frequently intended for human occupancy,such spaces may be devoted to the storage of food or other goodsrequiring a closely-controlled ambient.

The ducts comprising the air handling unit are constructed and arrangedfor drawing outdoor ambient air into the space, for exhausting air fromthe space to the outdoor ambient and for controllably mixing intake andreturn air. Such air handling units are equipped with adjustable dampersfor controlling the flow of air and include heat dissipating orabsorbing coils formed of tubing placed in the air flow path within theduct. These coils may be arranged in two sets, one each for flowingheated or chilled water or refrigerant therethrough, thereby permittingthe duct air temperature to be raised or lowered. Valves are providedfor controlling water flow. These dampers and valves may be controllablypositioned by load devices such as motorized rotary actuators coupledthereto.

In the alternative, a water-type heater coil may be replaced by a groupof electrically-powered heater strips which may be energized in one ormore stages for air heating. These heater strips may be energized by aload device such as a sequencer in response to command signals receivedby it. Control of the load devices, the exemplary actuators andsequencers, may be in discrete stages or in a continuum.

In systems of this type, energy savings may be realized by incorporatingeconomizing functions within the control scheme. For outdoor airtemperature and humidity which fall within a predetermined band oftemperature and humidity values, the cooling effect inherent in theoutdoor air may be utilized for appropriate conditioning of the spacewhile yet avoiding the expenditure of supplemental energy for thisfunction.

One type of microcomputer-based zone controller incorporates a smallnumber of resistive elements, the output signals of which are used bythe controller for selecting the desired setpoints of certain processparameters or for sensing temperature and relative humidity values. Suchcontrollers are arranged around a centralized intelligence concept; thatis, the data management and computational algorithms are embodiedexclusively in the controller microcomputer or microprocessor andassociated memory functions. The load devices to be connected to andoperated by the controller include no provision for device programming,memory function or communication with the controller. Such a controllerincorporates one or more multiplexers for sequentially directing sensedand setpoint parameters to a microcomputer for processing. Signals soprocessed are inverted and used to selectively energize one or more of aplurality of controller-mounted electromagnetic relays for actuatingstaged heating, cooling or a combination thereof. Other signals as, forexample, from a heat/cool changeover switch are inverted, directed to acomparator network and used to positionably control a rotatable actuatorfor powering outdoor air dampers. A potentiometer is used to select thatactuator position which provides the minimum air flow required forventilation. With such a controller, each heating and/or cooling stagewould be coupled to a predetermined set of relay output contacts by apair of wires, both the contacts and the wire pair associated therewithbeing dedicated solely to the task of controlling the particular stagecoupled thereto. Economizer control by a method known as differentialenthalpy may be accomplished only by connection of a separate enthalpycontrol module to the controller. An example of such a zone controlleris shown and described in U.S. Pat. No. 4,347,712.

While such zone controllers have hitherto provided a satisfactory meansfor controlling HVAC equipment, they tend to be characterized by certaindisadvantages. In particular, each controller relay contact is requiredto have a pair of dedicated wires coupled between it and the associatedheating or cooling stage. The analog output terminals for controllingthe economizer motor are likewise required to have a pair of dedicatedconductors coupled thereto. Since the distances between the controllerand the economizer motor or heating and cooling stages may besubstantial, the cost of installing this wiring, eight or moreconductors in all, may be quite significant. Additionally, thecontroller microcomputer, having a predetermined number of input/outputports, may be bound by the number of such ports to a maximum number andtype of load devices connected to the controller. Therefore, if aprocess control application requires an output configuration other thanthat which may be available from the predetermined number of relayoutput contacts and analog output terminals, it will be necessary tomodify the controller and its self-contained hardware in order toaccommodate the controller to such an application. It is difficult orimpossible to adapt a controller of this type to a system wherein thecombined number of heating and cooling stages exceeds the relativelylimited number of electromagnetic output relays embodied in thecontroller. Another disadvantage of such a controller relates to thefact that HVAC air handling units tend to have varying numbers ofheating, humidifying and/or cooling stages required from application toapplication. Notwithstanding, it may be highly desirable from comfortand energy conservation standpoints to cause the progressiveenergization or de-energization of the heating and cooling stages tooccur in evenly-spaced increments across the width, in temperaturedegrees, of the heating or cooling proportional bands, irrespective ofthe width of these bands or of the number of heating or cooling stages.Known zone controllers are somewhat inflexible and therefore not easilyadapted to such operating environments.

Yet a further disadvantge of a controller of this type which uses asystem of centralized intelligence is that no means are included wherebythe controller may selectively poll or otherwise communicate with theload devices coupled thereto. The controller is therefore unable toidentify, by digitally coded signals, the precise type of load devicecoupled thereto nor to interrogate and receive signals from the loaddevices indicative of their respective positions or status.

A zone controller which utilizes a microcomputer and is adapted tocontrol microcomputer-based load devices such as actuators andsequencers to form a system having distributed intelligence, which iscapable of communicating with any one or all of a plurality of such loaddevices by a single, two-wire communication bus coupled therebetween,which is adapted to communicate with such load devices by a pair ofmicrocomputer digital signal input/output (I/O) ports and which isadapted to communicate with a central processing unit at a higherhierarchical level would be a significant advance over the prior art.

SUMMARY OF THE INVENTION

In general, the electrically-powered zone condition control apparatus ofthe present invention includes a first multiplexing means adapted forreceiving analog status signals emanating from a plurality of passivesignaling devices such as temperature or humidity sensors orpotentiometers and transmitting these status signals in multiplexfashion to computing means such as an analog-to-digital converter. Theconverter changes these analog status signals to digital data signalsand directs them to computing means such as a microcomputer. A secondmultiplexing means receives binary input signals which may indicate, forexample, that an electrical contact is open or closed and also transmitsthese signals in multiplex fashion to the computing means. Themicrocomputer is adapted to perform algorithmic decisional functionsrelative to the signals received therein and is adaptable toperiodically, selectively transmit digital output signals to one or moreof a plurality of digitally-addressable load devices coupled to it by atwo-wire communication bus. The microcomputer is also adaptable toperiodically receive digital input signals from one or more of the loaddevices.

A method for controlling an environmental condition in a zone includesthe steps of generating a plurality of signals representative of thestatus of a plurality of signalling devices, converting selected statussignals to digital data signals and directing the data signals andunconverted status signals to a computing means such as a microcomputer.The microcomputer performs algorithmic decisional functions relative tothe signals received thereat and periodically, selectively transmitsdigital output signals along a communication bus to one or more of aplurality of uniquely, digitally addressable load devices. Digital inputsignals are periodically received from one or more of the load devices.

In a preferred embodiment, the controller includes a power supplyadapted to receive an input voltage of 24VAC and generate a plurality ofoutput voltages for utilization throughout the controller. The firstmultiplexing means includes a first multiplexer, a second multiplexerand a third multiplexer, the first multiplexer being adapted to receiveanalog voltage signals from a plurality of control parameter sensorssuch as those used to sense temperature and/or humidity. The secondmultiplexer receives analog voltage signals representative of the statusor settings of a first group of potentiometers while a third multiplexersimilarly receives analog voltage signals representative of the statusor settings of a second group of potentiometers. As commanded by thecomputing means, the first, second and third multiplexers seriallytransmit analog status signals to converter means embodied as ananalog-to-digital converter. The converter means is adapted to convertthe analog status signals to digital data signals representative ofthose status signals and direct the data signals to the microcomputer.The controller also includes second multiplexing means adapted toreceive a group of binary status signals and serially transmit thosesignals to the microcomputer upon its command. A signal-amplifyingbuffer circuit is coupled between the microcomputer and the level 1communication bus which links the controller with a plurality ofmicroprocessor-based, controlled load devices.

Optionally, the controller may also include a second buffer circuit forlinking the controller with a master controller at a higher hierarchicallevel by a level 2 communication bus. If the zone controller is solinked, it preferably includes address selection means whereby a usermay select any one of a plurality of digitally-coded addresses to whichthe controller will be responsive to a higher level controller coupledthereto by the level 2 bus.

The preferred controller is capable of receiving, upon request, codedsignals from a sequence panel coupled to the controller by the level 1bus, such signals representing the number of electromagnetic relaysembodied in the sequence panel and available for the control of heatingand/or cooling stages. The controller is adaptable to automaticallycause these stages to be energized and de-energized in predeterminedincremental spacing including evenly spaced increments across theheating or cooling proportional bands.

It is an object of the invention to provide a zone condition controllerwhich is adapted to control microcomputer-based load devices in acondition control system having distributed intelligence.

Another object of the invention is to provide a controller which iscapable of communicating with any one or all of a plurality of such loaddevices by a single, two-wire communication bus coupled therebetween.

Yet another object of the invention is to provide a controller which isadapted to communicate with microcomputer-based load devices by a pairof microcomputer digital signal input-output ports.

Still another object of the invention is to provide a controller adaptedto communicate with a master controller at a higher hierarchical level.

Another object of the invention is to provide a condition controllercapable of receiving both analog and digital status signals fromtemperature and humidity sensors, setpoint potentiometers, relaycontacts and the like.

Another object of the present invention is to provide a general purposecontroller capable of being adapted to a wide variety of controlstrategies by effecting a change only in the microcomputer programming.

Yet another object of the present invention is to provide a zonecontroller adaptable to automatically cause heating and/or coolingstages to be energized and de-energized in increments of predeterminedspacing across the heating or cooling proportional bands. These andother objects of the invention will become more apparent from thedetailed description thereof taken with the accompanying drawing.

DESCRIPTION OF THE DRAWING

FIG. 1 is a simplified pictorial view of a typical air handling unit towhich the controller of the present invention may be coupled;

FIG. 2 is a simplified electrical schematic diagram showing theinventive controller coupled to a plurality of load devices by acommunication bus;

FIG. 3 is a simplified electrical schematic diagram of the controller ofthe present invention;

FIGS. 4A and 4B, taken together, comprise the electrical schematicdiagram of the first multiplexer means and circuitry associatedtherewith, all forming a portion of the controller of the presentinvention;

FIG. 5 is a graphic depiction of the relationship of certain voltageinput signals to the first multiplexing means to corresponding voltageoutput signals therefrom;

FIGS. 6A and 6B, taken together, comprise the electrical schematicdiagram of the converter means, computing means, second multiplexermeans and circuitry associated therewith, all forming another portion ofthe controller of the present invention;

FIG. 7 is an electrical schematic diagram of the power supply portion ofthe inventive controller;

FIG. 8 is an electrical schematic diagram of the buffer interfacingcircuits of the controller;

FIGS. 9A and 9B, taken together, comprise the electrical schematicdiagram for a service module, a type of load device useful with thecontroller of the present invention;

FIG. 10 is a front elevation view of a sequence panel, another type ofload device useful with the controller;

FIGS. 11A and 11B, taken together, comprise the electrical schematicdiagram of the chassis of the sequence panel of FIG. 10, and;

FIG. 12 is a graphical representation depicting certain operatingaspects of the controller.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 1, the zone condition controller 10 is shown in connection withan air handling unit 11 which is utilized to control the temperatureand/or humidity in a conditioned space 13 such as, for example, asupermarket, small group of offices, or the like. A typical air handlingunit 11 is formed of sheet metal constructed and arranged to define aplurality of passageways or ducts 15, each having a square orrectangular cross-section. The air handling unit 11 includs a first duct17 for directing air from the outdoor ambient to the space, a secondduct 19 for exhausting air from the space to the outdoor ambient and across duct 21 for air mixing. Fans 23 are provided for air movement. Theducts 15 include louvered dampers 25 which may be positioned forcontrolling the amount of air flowing therethrough. Disposed within thefirst duct 17 is a plurality of electrically-powered heater strips 27which, when energized, heat the air which is discharged into the space13. The first duct 17 also includes a chiller coil 29 disposed thereinfor air cooling. The amount of cooling fluid flowing through the chillercoil 29 and the position of the dampers 25 may each be independentlycontrolled by a load device 31 as, for example, a motorized rotaryactuator. Selective energization of the heater strips 27 is by anothertype of load device, a sequence panel 33 described below. The loaddevices 31 are preferably microcomputer-based and are adapted to receivedigital command signals from the controller 10 by a two-wire, level 1bus 35 linking the controller 10 and the load devices 31. The loaddevices 31 are also adapted to transmit certain signals to thecontroller 10 via the bus 35. An example of a suitable load device 31embodied as a microprocessor-based rotary actuator is shown incontinuation-in-part U.S. Pat. No. 4,534,511, entitled "ControllableRotary Actuator" which was patented on Apr. 22, 1986, and is assigned tothe same assignee as this invention. The aforementioned application isincorporated herein by reference.

A temperature sensor 37 is disposed in the first duct 17 adjacent thecooling coil 29 for transmitting an analog signal to the controller 10which is representative of the temperature of the air being dischargedinto the conditioned space 13. A setpoint potentiometer 39 may bedisposed within the space 13 for selection of the temperature which isdesired to be maintained therein. As will be apparent from the followingdescription, this and other setpoint potentiometers may be incorporatedinto the controller 10 itself to help prevent unauthorized adjustmentthereof. Additionally, one or more humidity sensors (not shown) may bedisposed in the space 13 for sensing the relative humidity therein.

Referring now to FIG. 2, the controller 10 is shown to be coupled to alevel 1, two-wire communication bus 35 to which is attached a pluralityof load devices 31. In addition to the actuators and sequencersdescribed above, these load devices 31 may include a status panel 41, aservice module 42 and/or additional sensors (not shown) which may beconstructed using microcomputer-based circuitry and such "intelligent"sensors would thereby be capable of generating and transmitting digitalsignals back to the controller 10 via the bus 35 in response tocontroller signals. It should be appreciated that the mixture of loaddevices 31 coupled to the level 1 bus may include any combination ofthose types of devices described above. Further, the disclosedcontroller 10 is capable of communicating with up to 24 such loaddevices 31 and the use of a repeater would permit an even greater numberof load devices 31 to be utilized.

The controller 10 is adapted to receive a first group of analog voltagesignals at a first group of input terminals 43, the terminals 43 beingwired to sensors such as sensor 37 which generate these voltage signalsin response to the temperature or humidity of the air immediatelysurrounding the sensor. The controller 10 also includes a second groupof input terminals 45 adapted to be wired to resistive devices such aspotentiometers in order that a second group of analog voltage signalsrepresentative of the status or settings of those potentiometers may bereceived into the controller 10.

The controller also includes a third group of input terminals 47 forreceiving binary input signals, typically indicative of the energized orde-energized state of an item of equipment associated with the HVACsystem. For example, such a binary input signal may indicate whether ornot a fan, pump or humidifier motor is operating.

Briefly stated, the controller 10 functions to compare the desiredtemperature or humidity at a particular location in the system, space 13for example, and as represented by a setpoint signal with the actualtemperature or humidity at the same location and as represented by thesensor signals. Based upon the results of that comparison, thecontroller 10 selectively generates error signals and transmits anappropriate command or group of commands by specific address to one ormore of the load devices 31 coupled to the bus 35. Such command signalsare generated to cause system adjustments which will reduce or eliminatethe error between the signals being compared.

In FIG. 3, the controller is shown to include a power supply 49 forproviding a plurality of output voltages to the controller 10. A firstmultiplexing means 51 is coupled to the power supply 49 and is arrangedfor receiving analog status signals emanating from a plurality ofsignaling devices such as temperature or humidity sensors orpotentiometers and transmitting these status signals in multiplexfashion to an analog-to-digital converter 53. The converter 53 changesthese analog status signals to digital data signals and directs them tocomputing means 55 such as a microcomputer. A second multiplexing means57 receives binary input signals along a first channel 59 and theseinput signals may indicate, for example, that an electrical contact isopened or closed. These binary signals are similarly transmitted inmultiplex fashion to the computing means 55. Referring additionally toFIG. 2, the preferred controller 10 is also equipped with circuitrywhich permits several such controllers or other digitally-addressabledevices to be linked by a level 2 bus 61 to a central processing unit(CPU--not shown) located at a higher hierarchical level. By properlycoded address signals, the CPU may selectively communicate with any oneof the controllers or devices linked thereto. Accordingly, thecontroller 10 also includes an address selection means 63 whereby a usermay select any one of a plurality of digitally-coded address signals,preferably eight, to which the controller 10 will be responsive whensuch a CPU-generated signal is received by the controller 10 from thelevel 2 bus 61.

At certain times during the operation of the controller 10, it ispreferable to generate a reset signal for bringing the controllermicrocomputer 55 to a predetermined state. Internal reset is desirableupon the first application of power to the controller 10 as well asperiodically thereafter and, accordingly, a reset circuit 65 is providedfor generating such signals.

An optional feature of the controller 10 is the provision of anelectromagnetic relay 67 which may be discretionarily used by the systeminstaller. The relay contact 69 may be used, for example, to operate afan or may be used to sound an alarm in the event of a controllermalfunction.

The controller microcomputer 55 is coupled to the level 1 bus 35 by atransmit-mode amplifying buffer circuit 71 which converts the very lowpower digital signals emanating from the microcomputer 55 into digitalsignals of a power level sufficient to operate the load devices 31coupled to the bus 35. A receive-mode buffer circuit 73 conditions bussignals to a digital form unimpaired by spurious noise for bestutilization by the microcomputer 55. In the event that it is desired touse the zone controller 10 in conjunction with a CPU linked thereto bythe level 2 bus 61, the controller 10 also includes an amplifying buffercircuit 75 to facilitate such communications.

More particularly and referring next to FIGS. 4A and 4B, the firstmultiplexing means 51 is shown to include a first, master multiplexer 77adapted to receive analog voltage signals from a plurality of sensors 79such as temperature and/or humidity sensors. It is preferred that suchtemperature sensors are of the precision silicon type such as AmperexKTY81B1 having a voltage output range of 1VDC-2VDC over the full rangeof temperature to be sensed. A temperaure sensor product suitable foruse with the controller is available from Johnson Controls, Inc. undercatalog nos. A960 and T960. A preferred relative humidity (RH) sensor ortransmitter will likewise have a voltage output range of 1VDC-2VDC overthe full range of humidity to be sensed. Controller input signalsresulting from the activity of these sensors is capable of beingresolved to 13 bits. A plurality of reference resistors 80 are providedto linearize the output voltage of thermistor sensors of a type mostcommonly used. In the alternative, any type of sensor having a voltageoutput may be coupled to any one of the sensor input terminals so longas the output voltage of the sensor is in the preferred range of1VDC-2VDC over the full range of the parameter sensed, e.g., from 0% to100% relative humidity or -40° F. to 216° F. air temperature. Eachsensor input line is provided with a resistor-capacitor filter network81, for filtering electrical noise from the sensor signals as they aredirected to the first multiplexer 77.

The controller also includes a second multiplexer 83 and a thirdmultiplexer 85 for receiving, respectively, status or settings from afirst group of setpoint potentiometers 87 and from a second group ofsetpoint potentiometers 89. These potentiometers 87, 89 may be adjustedto select a wide variety of system control parameters as, for example,the zone setpoint temperature desired to be maintained in the space 13during periods of human occupancy. Other parameters include the set-uptemperature to be maintained in the space 13 during periods ofnon-occupancy and in those seasons when cooling is normally required andthe set-back temperature to be maintained in the space 13 during periodsof non-occupancy and in those seasons when heating is normally required.It should be appreciated that the set-up temperature will be severaldegrees higher than the zone setpoint temperature during those seasonswhen cooling is required to maintain the latter. Similarly, the set-backtemperature will be several degrees lower than the zone setpointtemperature during those seasons when heating is required to maintainthat nominal space temperature comfortable to the occupants. Otherparameters which may be selected by potentiometer settings include thebandwidth, in degrees Fahrenheit, of the cooing and heating deadbands,of the cooling and heating proportional bands, low and high airtemperature limits and the like. While the aforementioned setpointpotentiometers 87, 89 may be separately supplied and mounted by theuser, a preferred controller 10 will be adapted to include a pluralityof plug-in contacts 90 for receiving a subassembly having therein aplurality of individually adjustable potentiometers. The user willthereby find it convenient to make all setpoint adjustments directly atthe controller 10.

The controller circuitry is arranged so that the potentiometer signalsapplied to the input terminals 91 are resolved to nominal 12 bitaccuracy. Each input line has a pull-up resistor 92 coupled thereto.These resistors 92 preferably have a value selected to be sufficientlylow to maintain the voltage on an open input terminal 91 atapproximately the value of the VC5 voltage applied at the terminal 91aand yet sufficiently large to result in negligible loading of thesetpoint potentiometers 87, 89. It is preferred that each potentimetersinput terminal 91 be coupled to its associated multiplexer 83 or 85through a resistor-capacitor circuit 93 for filtering electrical noise.

In a preferred embodiment, the voltage applied at the terminal 91a is5VDC and the second and third multiplexers 83, 85 will be operative togenerate serially-transmitted analog signals for all setpoint voltagesfalling within the range 0-5VDC. Notwithstanding the generation ofmultiplexed signals in that range, the microcomputer 55 is programmed torecognize only those digital signals representative of potentiometervoltage signals occurring within the narrower first range of0.5VDC-4.5VDC. Voltage signals falling outside of this range will havepredetermined default values substituted therefor by the microcomputer55.

Signals emanating from the second multiplexer 83 and the thirdmultiplexer 85 are directed to the first multiplexer 77 through anamplifying means 94 having a high input impedance, a unity gain firststage 95 and a second, fractional gain inverting stage 97. Resistors 99are provided for setting the attenuation value of the inverting stage 97while the power supply voltage applied to terminal 101 acts as areference voltage for enabling voltage summations to provide DC levelshifting. The output of the amplifying means 94 is directed to the firstmultiplexer 77 which multiplexes all analog signals to the converter 53.

In a preferred controller 10, voltage summation and DC level shiftingand inversion circuitry is incorporated so that the representativeanalog signals received by the first multiplexer 77 from the second andthird multiplexers 83, 85 and directed to the converter 53 will occur inthe second range of 2VDC to 1VDC for all values of potentiometer voltagesignals occurring in the range of 0.5VDC-4.5VDC as well as for thosepotentiometer voltage signals occurring in the 0VDC-0.5VDC and4.5VDC-5.0VDC ranges. As prior stated, voltage signals occurring inthese latter two ranges will cause the computer means 55 to substitutepredetermined default values. This concept will be better appreciated byreference to FIG. 5 which illustrates the relationship of thepotentiometer voltage signals occurring within the first range 103 andthe default-triggering voltage signals occurring at the band edges 105of the first range 103, both of which are re-formed to voltage signalswithin the second range 107.

Referring next to FIGS. 6A and 6B, the controller 10 further includesconverter means 53 preferably embodied as an analog-to-digital converterfor receiving analog status signals occurring within the second voltagerange 107, converting these signals to digital data signalsrepresentative thereof and directing the data signals to a computingmeans 55 such as a microcomputer. An integration capacitor 109 iscoupled to the converter 53 for permitting the use of dual-slopeintegration conversion therewithin. The reception of a signal having avalue outside the second range 107 of 2VDC-1VDC will represent anoverload to the converter 53. It is thereupon necessary to immediatelydischarge the capacitor 109 to a voltage value which is sufficiently lowto permit the capacitor 109 to correctly perform its integrationfunction. Accordingly, an overload recovery circuit 111 is providedwhich includes a comparator 112 and a field effect transistor 112, thelatter being coupled to the capacitor 109. Upon the conclusion of eachintegration period, the transistor 112 is gated to a conducting statefor approximately five milliseconds for causing the rapid discharge ofthe capacitor 109. The converter 53 is clocked by a crystal 114 having afrequency selected to maximize the rejection of spurious 60 Hzelectrical noise.

The microcomputer 55 stores data signals, performs algorithmiccomputations with respect thereto and generates output signals which aredirected to the transmission line 115 comprising a portion of the level1 bus 35. These output signals may be of a first type for commanding aload device 31 to execute a particular function. For example, a loaddevice 31 comprising a rotary actuator may be commanded to incrementallyrotate its output shaft, thereby further opening or closing an airdamper 25. In the alternative, the output signals may be of a second,interrogating type whereby a load device 31 is caused to transmitcertain information back to the controller 10 along the reception line116 which is part of the level 1 bus 35. An example of a load deviceresponse resulting from the reception of an interrogating command wouldbe the transmission of a binary coded message which represents theactual angular position of an actuator shaft. Yet a third type of outputsignal may be generated by the controller for resetting all load devices31 to a known, predetermined state.

In a preferred embodiment and as explained above, the controller 10 isarranged for receiving a plurality of analog voltage signals, preferablysix in number, at a first group of input terminals 43 which are adaptedto be wired to sensors. Additionally, the controller 10 is adapted toreceive a plurality of second analog voltage signals, preferably sixteenin number, at a second group of input terminals 91 adapted to be wiredto groups 87, 89 of potentiometers. The microcomputer 55 is programmedto cycle at approximately a one-second time period and during eachcycle, the controller 10 accepts and stores digital data signals whichare representative of the analog voltage signals of all six sensors 79and of all binary input signals received at the third group of inputterminals as described below. Digital data signals representative of theanalog voltage signals of two potentiometers are also stored during eachcycle. Data signals representative of the settings of otherpotentiometers are also sequentially accepted and stored, two suchsignals for each consecutive cycle and therefore, upon the occurrence ofeight consecutive cycles, the microcomputer 55 will have sequentiallyaccepted and stored one set of data signals representative of the analogvoltage signals of each of all potentiometer groups 87, 89, eight setsof data signals representative of the binary input signals and eightsets of data signals, each of the latter set being representative of thevoltage signals of all sensors 79.

The third group of terminals 47 for receiving binary input signals iscoupled to a second multiplexing means 57 for generation of serialanalog signals to be directed to the converter 53. An address selectionmeans 63 is connected to the second multiplexing means 57 and ispreferably embodied as a plurality of slide action switches, three innumber, for permitting the selection of any one of eight possibleaddresses to which the controller 10 will be responsive if a message soaddressed is received thereat along the level 2 bus 61. Pull-upresistors 117 are coupled to the input terminals 47 for permitting theseterminals to be activated by either the closure of an external switchcontact or by a digital logic "0" signal. Filtering of unwantedelectrical noise is accomplished by the inclusion of aresistor-capacitor network 119 coupled to each input terminal.

Since the proper performance of the microcomputer 55 may be impaired bythe presence of transient voltages applied to or induced within itscircuit nodes, it is desirable to provide means by which themicrocomputer 55 may be periodically reset. Reset is also preferred forbringing the microcomputer 55 to a predetermined state at that time whenpower is initially applied to the controller 10. Accordingly, thecontroller 10 also includes reset means 121 for periodically generatinga reset signal and directing such signal to the microcomputer 55. Themicrocomputer 55 of a preferred controller 10 will be programmed toperform a review of the integrity of the data stored therewithinimmediately subsequent to the receipt of the reset signal.

More specifically, the receipt of an internal reset signal at themicrocomputer 55 will initiate a start-up routine which includes thesteps of self-checking for proper function, accepting and storingdigital signals representative of the binary state of the input signalsreceived at the third group of terminals 47 and of those signals beinggenerated by the address selection means 63. The self-checking stepincludes a test of random access memory (RAM) to verify the accurancy ofall data, both incoming to the microcomputer 55 and calculatedtherewithin. Subsequent steps include accepting and storing digitalsignals representative of the values of a plurality of sensor andpotentiometer analog voltages, switching the level 1 bus 35 to a logic"0" condition for a predetermined period of time and switching the level1 bus 35 to a logic "1" condition for a predetermined period of time. Ina preferred embodiment, these time periods will be approximately onesecond each and will result in a resetting of the load devices 31 and averification of the operation of the transmit and receive functions.Thereafter, the microcomputer 55 transmits a first set of digital outputsignals comprising a plurality of polling or interrogating messages,each one of which is unique to each of all possible addresses of theremote load devices 31 which may be coupled to the controller by thelevel 1 bus 35. The microcomputer 55 then receives and stores theaddress of each responsive load device 31 and thereafter transmitsdigital output signals only to those load devices 31. Additionally, theaddresses of non-responsive devices are periodically polled and if ananswering response is generated, digitally-coded addresses of respondingdevices are likewise stored.

The controller 10 also includes an optional relay circuit 123 forselectively actuating an electromagnetic relay 67. The circuit 123includes a transistor 125 for energizing the relay coil 127, acurrent-limiting resistor 129 and a diode 131 for protecting thetransistor 125 from voltage spikes which may occur when the coil 127 isde-energized. The relay contacts 132 may be used for operating anexternal fan, for sounding an audible alarm or the like.

Referring next to FIG. 7, the power supply 49 is shown to includeterminals 133 for receiving an input voltage, preferably 24 VAC, and aplurality of output terminals 134 for powering various portions of thecontroller 10. The power supply 49 includes a half-wave, negativeregulated supply section 137 and a regulated, switching positive supplysection 139. A first regulator 140 maintains a voltage at its outputterminal which is nominally 8 VDC in the preferred embodiment. Theillustrated circuitry functions to switch the transistor 141 to aconducting state whenever the output voltage of the regulator 140 fallsbelow the predetermined regulated value. The regulator 140 is thereuponpartially bypassed by a current flowing through the inductor 142 to thecapacitor 143. If the voltage at the capacitor 143 exceeds thepredetermined regulation value, the transistor 141 is switched to anonconducting state. The output of the first regulator 140 is coupled tothe input of a second regulator 144 for providing a regulated outputvoltage at nominally 5 VDC. A capacitor 145 is coupled to the outputterminal thereof for providing transient stability, a plurality ofresistors 146 define a voltage divider network for providing a pluralityof reference voltages while a capacitor 147 provides noise filtering.

Referring next to FIG. 8, there is shown a first interface circuit 149and a second interface circuit 151 for rejecting several types ofspurious electrical noise which may interfere with communications. Theseinterface circuits 149, 151 permit the microcomputer 55 to transmit andreceive signals on both the level 1 bus 35 and the level 2 bus 61.Interfacing between the microcomputer 55 and the buses 35, 61 is asshown in FIG. 8 taken in conjunction with FIGS. 6A and 6B.

Referring to FIGS. 2, 9A and 9B, one type of load device which is usefulwith the present invention includes a service module 43 for providingsystem setup and troubleshooting functions. A preferred service module43 is constructed and arranged to operate in either a command, anoverride or a monitor mode. When used in the command mode, the level 1bus 35 is disconnected from the interface circuit 149 of FIG. 8, theservice module 43 is connected to the level 1 bus 35 and may thereuponbe utilized to generate commands to the load device 31. For example,depression of a predetermined combination of buttons 151 disposed uponthe service module 43 will cause the generation of a command signalrequesting a microcomputer-based temperature sensor (not shown) totransmit a digital signal representative of the sensed parameter. Thedigitized signal from the responding sensor is displayed upon the moduleluminary 153, preferably in engineering units, e.g., degrees Fahrenheit.If the service module 43 is used for generating override commands duringthose times when the level 1 bus 35 is connected to the controller 10, apreferred module 43 is capable of generating such commands as, forexample, to override the controller 10 and bring a rotary actuator shaftto a new position. It is apparent then, that the service module 43 iscapable not only of detecting and displaying data stored within thecontroller 10 but is also capable of generating command signals forpositioning load devices 31, either singly or in plural.

When used as a monitoring device, the service module 43 receives alldigitally-coded information being transmitted on the level 1 bus 35,irrespective of whether such transmission is by the controller 10 or bya responding load device 31. Depression of a predetermined sequence ofmodule buttons 151 will permit the module 43 to receive ad display anymessage appearing on the bus 35.

From the foregoing description, it will be appreciated that the user mayemploy the controller 10 in conjunction with a service module 43 tocontrol a condition in a zone as, for example, the zone temperature orhumidity. Control in this manner may be setup, troubleshooting or otherpurposes. A method for controlling a zone condition in this manner wouldinclude the steps of providing a controller 10 coupled to a plurality ofload devices 31 by a communication bus 35, providing a service module 43coupled to the bus 35, generating a controller-originated signal forcommanding a load device 31 to a first position, receiving amodule-originated override signal within the controller 10 andgenerating a controller-originated override signal for commanding theload device 31 to a second position.

Yet another type of load device useful with the controller 10 of thepresent invention is shown in FIGS. 1, 10, 11A and 11B to include asequence panel 155 for selectively controlling heat transfer stages suchas heating stages 27, cooling stages 29 or a combination thereof. Apreferred panel 155 includes a sequencer chassis 157 and one or morerelay packs 159, the latter for controllably actuating the stages 27,29. Referring particularly to FIGS. 11A and 11B, the chassis 157 isshown to include a regulated, switching positive supply section 161 forproviding power to the chassis microprocessor 163. The section 161 isclosely similar to the section 139 shown in FIG. 7 but includes anadjustable regulator 165 in place of the fixed regulator 144 shown inthe latter FIGURE. An interface circuit 167 facilitates substantiallynoise-free communication between the level 1 bus 35 and themicrocomputer 163 to which it is coupled. Referring additionally to FIG.10, a first group of terminals 169 is provided for facilitating theelectrical connection of a first electromagnetic interface deviceembodied as a relay pack 159. Additional second, third and fourth groupsof relay pack terminals, 170, 171, and 172 respectively, permit theconnection of yet other relay packs (not shown) if such are required forthe application. Each relay pack 159 includes a known plurality ofelectromagnetic relays, preferably four, each relay having its contactsmade available at external spade terminals 173 and internally connectedas shown in FIG. 10. It is convenient to construct the panel 155 toinclude a housing 175 having mounting holes 177 adapted to receive oneor two relay packs 159 atop the housing 175. Additional relay packs 159may be wall mounted adjacent the housing. Connection of the relay packs159 to the groups of terminals 169-172 is by multiconductor wireassemblies and edge mounted terminal strips (not shown) located at theupper end and lower end of the housing 175. A plurality of screwterminals 179 is provided for connection of 24 VAC, level 1 bus 35 andground connections.

The sequence panel 155 includes a binary coded decade switch 181 forselecting the number of system heating stages to be controlled by one ormore relay packs 159. The chassis circuitry is configured such that thenumber selected at the switch 181 is equal to one-half the number ofheating stages in the system to be controlled. Additionally, the panelmicrocomputer 163 may be programmed for providing unalterable,predetermined system timing constraints. For example, the microcomputer163 may be programmed to provide a minimum time over which the coolingstages will be maintained in a de-energized state, once de-energizationoccurs. Similarly, minimum time periods may be programmed for providinga maximum number of cooling cycles per hour, of heating cycles per hour,for energizing any two consecutive heating stages or for maintaining aheating or cooling stage in a de-energized state.

However, in a preferred embodiment, the panel 155 is provided with aplurality of switches 184 whereby the user may select one of two timeconstraints which have been predetermined by the panel designer.

Each group of relay pack terminals 169-172 is coupled to a separateresistor 185, the purpose of which is to provide a signal to themicrocomputer 163 whenever a relay pack 159 is connected to a particularterminal group. The microcomputer 163 is programmed to read the numberof system heating stages as selected by the switch 181, read the numberof relay packs 159 connected to the terminal groups 169-172, each pack159 being assumed by the program to include four relays, subtract thenumber of heating stages from the total number of relays available andcontrol the remaining relays as being connected to cooling stages.

Referring next to FIG. 12, there is shown a zone temperature axis 187upon which has been superimposed certain vertical axes 189 to define,for example, the width in degrees of the heating and coolingproportional bands 191 and 193, respectively, heating and cooling deadbands 195 and 197, respectively, an economizer proportional band 199 andthe set point temperature 201 desired to be maintained within the zoneor space 13. A feature of the zone controller 10 is that itsmicrocomputer 55 may be programmed to distribute the actuation of thosecooling stages coupled to a sequence panel 155 in virtually any mannerover the temperature degree width of the cooling proportional band 193,notwithstanding the fact that the band 193 may have a variable width,within limits, as selected by the controller user. As an exemplaryillustration of this feature, it is assumed that the system controlledincludes two cooling stages, the first of which has an operatinghysteresis loop 203 and the second of which has an operating hysteresisloop 205, with the spacing of the loops 203, 205 being distributed, inthis example, evenly over the width of the proportional band 193. Whilenot illustrated, it should be appreciated that a preferred controller 10may likewise be programmed to distribute, evenly or unevenly, theactivity of the heating stages over the width of the heatingproportional band 191.

It is preferable that the program embodied in the panel microcomputer163 be configured to recognize separate addresses for the heatingfunction and for the cooling function. Optionally, the program may alsobe configured to recognize a third address used to control selectedelectromagnetic relays (not shown) which are under no time delay orother constraints. For example, a relay contact may be used to energizeand de-energize a fan in accordance with a suitable command received atthe third address.

When preparing to operate the controller 10 of the present invention andif a sequence panel 155 will be used in conjunction therewith, the panelswitches 181 and 184 are set in accordance with the configuration of theparticular air handling unit(s) 11 being controlled. If load devices 31embodied as actuators are used for analog positioning control of valvesand/or dampers 25, the address switches of each are appropriately set inaccordance with the particular function being controlled by it, i.e.,intake air, exhaust air or air mixing. The actuator is then caused torotate its output shaft to the extremes of its travel, the 0% and 100%travel positions, and the mechanical linkages between the actuator andthe device controlled, an exemplary damper 25, are then adjusted.

The program embodied in the controller microcomputer 55 is preferablyconfigured such that the addresses of each of all actuators will beselected from a first group of addresses, the addresses of each of allsequence panel heating stages will be selected from a second group ofaddresses and the addresses of each of all sequence panel cooling stageswill be selected from a third group of addresses. Similarly, particularsensors and set points will be programmed and assumed to be atpredetermined addresses.

Referring to FIGS. 1 and 2 and with the load devices 31 coupled to thelevel 1 bus 35, the bus 35 and sensors 79 coupled to the controller andthe setpoints selected by adjustment of the groups 87, 89 ofpotentiometers, power is applied to the system and the controller 10will thereupon function to controllably condition the temperature and/orhumidity in a zone.

A method for controlling the condition of a zone includes the steps ofproviding a zone controller 10 adapted to communicate with a level 1 bus35 having a plurality of load devices 31 coupled thereto, scanning andstoring the output values of a plurality of sensors 79 coupled to thecontroller 10 and scanning and storing the output values of a pluralityof setpoint devices 87, 89 coupled to the controller 10. Following thisscanning activity, the controller 10 generates a synchronous resetsignal for assuring proper operation of the controller microcomputerprogram. If the program is operating properly, the microcomputer 55 willanticipate and accept this reset signal and, upon so doing, will re-scanall values and parameters in memory such as those of sensors 79, setpoints and addresses. The controller 10 is programmed to compare thevalues and parameters existing prior to reset with those existing afterreset. If the compared values and parameters are identical before andafter reset, the controller 10 thereupon initiates operation of thecontrol algorithm. This initiating step preferably includes thegeneration of an initializing or polling message to each of everypossible address of load devices 31 that may be coupled to thecontroller 10, irrespective of whether a load device 31 is, in fact,coupled to the controller 10 at that address. Each coupled load device31 is thereupon caused to generate a responsive identifier signal whichincludes digital bits delineating the unique address of the respondingload device 31. The controller 10 thereupon compares all of the possibleaddresses of load devices 31 with those addresses of load devices 31actually coupled thereto and subsequently communicates only withaddresses of the latter. Thereafter, the controller 10 performsalgorithmic decisional functions relative to the signals receivedtherein, selectively transmitting digital output signals to one or moreof a plurality of uniquely, digitally-addressable load devices 31coupled thereto by a communication bus 35 and periodically receivingdigital input signals from one or more of these load devices 31.

During certain phases of operation of the controller 10, it may bedesirable to generate a signal for resetting all load devices 31 coupledto the level 1 bus 35. This may occur when, for example, there is aninterruption of power at the controller 10 but not at the load devices31. It may also be desirable to assure that the bus 35 is notinadvertently short-circuited. In these events and prior to the scanningsteps delineated above, the controller 10 generates a bus reset signalfor a first predetermined time of approximately one second by holdingthe bus 35 at a logic "0" value. The controller 10 also generates afault detection signal by switching the bus 35 to a logic "1" state fora second, predetermined time of approximately one second to assure thatno external device is causing an inadvertent short circuit upon the bus35.

In the event that a service module 43 is coupled to the level 1 bus 35,the operator may desire to cause the generation of an override signal orto read the value of a particular sensor 79 or set point value. If theoperator wishes to override an output signal from the controller 10, hemay sequentially depress certain buttons 151 disposed upon the servicemodule 43 whereupon the digital output signal is intercepted, a commandsignal is generated and directed to the controller 10 as a request for anew output signal based upon the override value selected by theoperator. The controller 10 will thereupon be caused to generate areplacement digital output signal based upon the override value.

The operation of the inventive controller 10 has been described inconnection with what is known in the HVAC art as a hot deck, cold decktype of air handling unit 11. However, it will be appreciated by thoseof ordinary skill in the art that the controller 10 is an apparatus ofbroad, general purpose application and the controller 10 may be readilyadapted for use with variable air volume (VAV) systems. Such systemsinclude, for cooling, a source of air at a temperature a few degreesless than that of the space to be cooled. The temperature of the sourceair is maintained relatively constant and the space is controllablycooled by varying the volume of air introduced thereto. The only changein the controller 10 which is required to permit its use with VAVsystems is a change in the programming of the microcomputer 55.

It is to be appreciated that wherever the terms "microcomputer" or"microprocessor" are used herein, they are intended to be synonymouswith a digital computing structure such as an integrated chip,irrespective of whether the memory function is incorporated therewith asan integral part or as a separate memory device coupled to thestructure. The following component values have been found useful in thecontroller of the present invention. Capacitance values are inmicrofarads unless otherwise specified; resistors are 5% and capacitorsare 20% tolerance unless otherwise specified.

    __________________________________________________________________________    FIGS. 4A, 4B                                                                  R26-R31   2320, 0.1%                                                                             R32-R37   100K                                             R38       69 8K, 1%                                                                              R39       10K, 1%                                          R40-R55   47K      R56-R71   270K                                             C10-C15, C46                                                                            0.22     C16-C31   0.022                                            C47       0.001    U5        CD4069B                                          U6        LM358    U7-U9     CD4051B                                          U14       LM308                                                               FIGS. 6A, 6B                                                                  R72-R82, R89, R94                                                                       4.7K     R83-R87   470K                                             R88,R93   1K       R90, R100 1 M                                              R91, R92  27K      R95       330                                              R96, R97  47K      R98, R99  100K                                             R101      10K      C32-C36   0.022                                            C37, C39, C92                                                                           0.22     C38       0.001                                            C40, C41  27 pf    C43       10                                               C44       0.15     C45       0.33                                             C48       0.1      D10-D13   1N4148                                           FIGS. 6A, 6B                                                                  Q4        2N3905   Q5        GES5822                                          Q6        J201     U5        CD4069B                                          U6        LM358    U10       CD4512B                                          U11       CD4024B  U12       MC6801-1                                         U13       1CL7109  Y1        4.9152 MHZ                                       Y2        3.5795 MHZ                                                          FIG. 7                                                                        D1, D2    1N5060   D3        1N4935                                           C1        330/50 V C2        22/50 V                                          C3        2.2/50 V C4        0.01                                             C5 100/16 V                                                                             low ESR  C6, C50   0.22                                             C49       0.1/200 V                                                                              R1        680                                              R2        33       R3        220                                              R4        100K     R5        1 M                                              R6        240      R7        1.3K                                             R10       2670, 0.1%                                                                             R11       90.9, 0.1%                                       R12       1060, 0.1%                                                                             R13       229, 0.1%                                        U1        79L05    U2        317L                                             U3        7805     Q1        2N6107                                           L1        350 microh.                                                         FIG. 8                                                                        D4        1N4736   D5, D6, D8, D9                                                                          1N4148                                           D7        1N5060   RT1, RT2  22, +t°                                   R14       470      R15, R21  10K                                              R16, R22  20K      R17, R23  47K                                              R18, R24  6.8K     R19, R25  330K                                             R20       100K     C7        0.22                                             C8, C9    0.0033 X7R                                                                             C51       0.022                                            U4        556      U5        CD4069B                                          Q2, Q3    GES5822                                                             FIGS. 9A, 9B                                                                  R1        2K       R2, R7    10K                                              R3        20K      R4        3.3K                                             R5        47K      R6        470K                                             R8        1 M      R9        10 M                                             R10, R14-R17                                                                            4.7K     R11       240                                              R12       2.7K     R13       1.2K                                             C1        0.0033 X7R                                                                             C2        0.01                                             C3        0.001 X7R                                                                              C4, C8    0.1                                              C5, C6    22 pf    C7        47, 50 V.                                        C9        100, 10 V.                                                                             RT1       10, +t°                                             low leak                                                            D1, D4-D6 IN5060   D2, D3    IN4148                                           Q1        GES5822  U1        ICM7555I                                         U2        CD4023B  U4        LM317L                                           U5        LM2931   U6        74C374                                           U7        NMC27C16 LDC1      PCI183                                           S2, S3    87AB3-201                                                                              U3        MC146805EZ                                       Y1        5 MHz                                                               FIGS. 11A, 11B                                                                R1        100K     R2, R18, R27-R30                                                                        10K                                                                 R53-R55                                                    R3        20K      R4        3.3K                                             R5        47K      R6-R8, R11                                                                              470K                                             R9        33       R10       100                                              R12, R17  1 M      R13       240                                              R14       1.3K     R15       768, 1%                                          R16       243, 1%  R19-R26, R31-R52                                                                        4.7K                                             C1        0.0033 X7R                                                                             C2        0.22                                             C3, C9    0.01     C4, C5, C11                                                                             0.10                                             C6        27 pf    C7        0.10, 250 V.                                     C8        330, 50 V.                                                                             C10       100, 16 V.,                                                                   low ESR                                          FIGS. 11A, 11B,                                                               D1, D6    5060     D7        4935                                             D2-D5     1N4148   RT1       22, +t°                                   Q1        5822     Q2        2N6107                                           Q3        5823     U1        556                                              U2        CD4069   U3        317L                                             U4        317T     U5        MC6805                                           Y1        4.00 MHZ 52        Model 230002G                                                                 by EECO Inc.                                     __________________________________________________________________________

While a single preferred embodiment of the zone temperature controllerand of a method for using same have been shown and described, they arenot intended to be limited thereby but only by the scope of the appendedclaims.

The computer program listing for the controller 10 is set forth asfollows: ##SPC1##

We claim:
 1. A method for controlling an environmental condition withina zone including:generating a plurality of signals representative of thestatus of a plurality of signalling devices; converting selected of saidstatus signals to digital data signals and directing said data signalsand unconverted status signals to computing means; performingalgorithmic decisional functions relative to said signals received atsaid computing means; transmitting digital output signals from saidcomputing means along a communication bus for reception by a pluralityof uniquely, digitally addressable load devices coupled to saidcommunication bus and adapted to effect control of a condition of azone, and; periodically receiving at said computing means digital inputsignals transmitted from at least one of said load devices.
 2. A methodfor controlling an environmental condition in a zone including:providinga zone controller incorporating a microcomputer and adapted tocommunicate with a level one bus having a plurality of uniquely,digitally addressable load devices coupled thereto; scanning and storingthe output values of a plurality of sensors and setpoint devices coupledto said controller; providing a reset signal for assuring properoperation of the program embodied in said microcomputer; rescanning andstoring said output values of said sensors and setpoint devices;comparing said output values existing prior to said reset signal withthose same values existing subsequent to said reset signal; initiatingoperation of a control algorithm embodied in said microcomputer forperforming algorithmic decisional functions relative to said outputvalues; selectively transmitting digital output signals to at least oneof said load devices for effecting control of an environmental conditionwithin said zone, and; periodically receiving digital input signals fromat least one of said load devices.
 3. The method set forth in claim 2wherein said initiating step includes the steps of generating a pollingmessage to each of every possible digital address for load devices thatmay be coupled to said bus;receiving and storing a responsive identifiersignal unique to the address of each load device actually coupled tosaid bus; comparing said possible digital addresses with said addressesresponsively received, and; thereafter selectively transmitting digitaloutput signals only to load devices actually coupled to said bus.
 4. Themethod set forth in claim 3 and further including the stepsof:generating a bus reset signal for resetting load devices coupled tosaid bus, and; generating a fault detection signal for assuring thatsaid bus is not inadvertently short circuited, said generating stepsoccurring prior to said scanning and storing step.
 5. The method setforth in claim 2 and further including the steps of:generating a busreset signal for resetting load devices coupled to said bus; generatinga fault detection signal for assuring that said bus is not inadvertentlyshort circuited, said generating steps occurring prior to said scanningand storing step.
 6. A method for controlling a condition in a zoneincluding:providing a zone controller incorporating a microcomputer andadapted to communicate with a level one bus having a plurality ofuniquely, digitally addressable load devices coupled thereto, said loaddevices including at least one sequence panel adapted to control heattransfer stages; determining the number of heat transfer stagescomprising heating stages coupled to said sequence panel; determiningthe bandwidth of a heating proportional band, and; controllablyactuating said heating stages in a manner to be substantially evenlydistributed across said bandwidth.
 7. The method set forth in claim 6further including the steps of;determining the number of electromagneticinterface devices incorporated into said sequence panel; subtractingsaid number of heating stages from said number of interface devices,said difference being representative of the number of cooling stagescoupled to said sequence panel; determining the bandwidth of a coolingproportional band, and; controllably actuating said cooling stages in amanner to be substantially evenly distributed across said coolingproportional band.